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Re: [Xen-devel] [PATCH] tools/xenstore: try to get minimum thread stack size for watch thread

On 02/22/2018 06:53 AM, Juergen Gross wrote:
When creating a pthread in xs_watch() try to get the minimal needed
size of the thread from glibc instead of using a constant. This avoids
problems when the library is used in programs with large per-thread

Use dlsym() to get the pointer to __pthread_get_minstack() in order to
avoid linkage problems and fall back to the current constant size if
not found.

Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
Only compile tested. Jim, can you please verify this patch is solving
your original problem?

It didn't help, but it could be due to my buggy glibc

# gdb xl
(gdb) r create test-hvm.xl
Starting program: /usr/sbin/xl create test-hvm.xl
Parsing config from test-hvm.xl
Program received signal SIGSEGV, Segmentation fault.
0x00007ffff72d51c2 in __pthread_get_minstack () from /lib64/libpthread.so.0
(gdb) thr a a bt

Thread 1 (Thread 0x7ffff7fd8780 (LWP 2568)):
#0  0x00007ffff72d51c2 in __pthread_get_minstack () from /lib64/libpthread.so.0
#1  0x00007ffff66ae259 in xs_watch (h=0x55555578fc90,
    path=path@entry=0x555555798fa0 "/local/domain/0/device-model/2/state",
    token=token@entry=0x5555557990b0 "3/0") at xs.c:826
#2  0x00007ffff79476f4 in libxl__ev_xswatch_register 
w=w@entry=0x555555797468, func=func@entry=0x7ffff793dd10 <xswait_xswatch_callback>, path=0x555555798fa0 "/local/domain/0/device-model/2/state") at libxl_event.c:638
#3  0x00007ffff793deb0 in libxl__xswait_start (gc=gc@entry=0x5555557955f0,
    xswa=xswa@entry=0x5555557973e0) at libxl_aoutils.c:53
#4  0x00007ffff79326b0 in libxl__spawn_spawn (egc=egc@entry=0x7fffffffd950,
    ss=ss@entry=0x555555797370) at libxl_exec.c:292
#5 0x00007ffff79258d3 in libxl__spawn_local_dm (egc=0x7fffffffd950, dmss=<optimized out>)
    at libxl_dm.c:2400
#6 0x00007ffff791d3a7 in domcreate_launch_dm (egc=0x7fffffffd950, multidev=0x555555798168,
    ret=<optimized out>) at libxl_create.c:1379
#7  0x00007ffff7967275 in libxl__bootloader_run (egc=egc@entry=0x7fffffffd950,
    bl=bl@entry=0x555555796cc0) at libxl_bootloader.c:403
#8  0x00007ffff791ffe3 in initiate_domain_create (egc=egc@entry=0x7fffffffd950,
    dcs=dcs@entry=0x555555796610) at libxl_create.c:997
#9  0x00007ffff79201a1 in do_domain_create (ctx=ctx@entry=0x55555578f2a0,
    d_config=d_config@entry=0x7fffffffdb70, domid=domid@entry=0x7fffffffdaa8,
restore_fd=restore_fd@entry=-1, send_back_fd=send_back_fd@entry=-1, params=params@entry=0x0,
    ao_how=0x0, aop_console_how=0x0) at libxl_create.c:1682
#10 0x00007ffff79204b6 in libxl_domain_create_new (ctx=0x55555578f2a0,
    d_config=d_config@entry=0x7fffffffdb70, domid=domid@entry=0x7fffffffdaa8,
ao_how=ao_how@entry=0x0, aop_console_how=aop_console_how@entry=0x0) at libxl_create.c:1885
#11 0x00005555555780b4 in create_domain (dom_info=dom_info@entry=0x7fffffffe0b0)
    at xl_vmcontrol.c:902
#12 0x00005555555790c4 in main_create (argc=1, argv=0x7fffffffe378) at xl_vmcontrol.c:1207
#13 0x0000555555560c5b in main (argc=2, argv=0x7fffffffe370) at xl.c:384

If you like, I can try a patched glibc after the weekend :-).


  tools/xenstore/Makefile |  4 ++++
  tools/xenstore/xs.c     | 19 ++++++++++++++++++-
  2 files changed, 22 insertions(+), 1 deletion(-)

diff --git a/tools/xenstore/Makefile b/tools/xenstore/Makefile
index 2b99d2bc1b..fb6c73e297 100644
--- a/tools/xenstore/Makefile
+++ b/tools/xenstore/Makefile
@@ -100,6 +100,10 @@ libxenstore.so.$(MAJOR): libxenstore.so.$(MAJOR).$(MINOR)
        ln -sf $< $@
+ifeq ($(CONFIG_Linux),y)
+xs.opic: CFLAGS += -DUSE_DLSYM
+xs.opic: LDFLAGS += -ldl
libxenstore.so.$(MAJOR).$(MINOR): xs.opic xs_lib.opic
-Wl,libxenstore.so.$(MAJOR) $(SHLIB_LDFLAGS) -o $@ $^ $(LDLIBS_libxentoolcore) 
diff --git a/tools/xenstore/xs.c b/tools/xenstore/xs.c
index abffd9cd80..8372f5b1a4 100644
--- a/tools/xenstore/xs.c
+++ b/tools/xenstore/xs.c
@@ -47,6 +47,11 @@ struct xs_stored_msg {
#include <pthread.h> +#ifdef USE_DLSYM
+#define __USE_GNU
+#include <dlfcn.h>
  struct xs_handle {
        /* Communications channel to xenstore daemon. */
        int fd;
@@ -810,12 +815,24 @@ bool xs_watch(struct xs_handle *h, const char *path, 
const char *token)
        if (!h->read_thr_exists) {
                sigset_t set, old_set;
                pthread_attr_t attr;
+               static size_t stack_size;
+#ifdef USE_DLSYM
+               size_t (*getsz)(void);
+ if (!stack_size) {
+#ifdef USE_DLSYM
+                       getsz = dlsym(RTLD_DEFAULT, "__pthread_get_minstack");
+                       stack_size = getsz ? getsz() : READ_THREAD_STACKSIZE;
+                       stack_size = READ_THREAD_STACKSIZE;
+               }
                if (pthread_attr_init(&attr) != 0) {
                        return false;
-               if (pthread_attr_setstacksize(&attr, READ_THREAD_STACKSIZE) != 
0) {
+               if (pthread_attr_setstacksize(&attr, stack_size) != 0) {
                        return false;

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